Fractionation of black grease



sept. 15, 1953 Alm/Www BW /M/gkefv M ATTORNEYS Patented Sept. 15, 1953 UNITED' STATES PATENT OFFICE FRACTIONATION OF BLACK GREASE jamin Glartnn Application May 9, 1950, Serial No. 160,978

16 Claims.

This invention relates to theffraetionation of black grease, andamore particularly, to a method by which high quality neutral oil and high quality fatty acids are recovered from black grease with a minimum or losses and: in which the agents employed. are recovered andl reused in the process.

Black greaseis, a product obtainedby the acidulation of soapstock from the1 alkali refining of crude fatty oils. Fatty oils such as vegetable and animal oils are conventionally reiined by treating the same with aqueous'solutions ofY alkalines such as caustic soda or soda ash. The aqueous alkali solution neutralizes the free fatty acids in the oil to form soap andprecipitates impurities such as gums and coloring matter. The soap and precipitated impurities along with excess alkali, water and a substantial quantity of entrained neutral oil are separated fromv the resulting refined oil by settling or centrifugal separation. The separated material is known as soapstock. A small amount oil materials known as unsaponiables also separateL with the soapstcck butl are usually consideredto be-a part of the entrained neutral oil.

The separated soapstoclr in theform in which it is separated may be sold' by the renner on the basis of total fattyy acida content to manufacturers of lowr gradesoap or'manufacturersof distilled fatty acids. treated at the reilnerylry` boiling with sulfuric acid to liberate the fatty acids from the soap without splitting the-gl'ycerldes off theentrained neutral oil and then separating water along with dissolved inorganic salts and excessV acidV from the impure fatty material. TheY resulting impure fatty material is known asacid oil or black grease and is usually sold to manufacturers of distilled fatty acids on the basis of total fatty acid content. Eitherthesoapstockor the black grease must be soldfora low price because of the difficulties encountered in recovering high quality fatty material therefrom by present commercial processes.

Black grease contains fatty` acids, neutral oil and the impurities above referred` to, namely, gums and coloring matter. The neutral oil content varies from l5 to 60% or more.- depending upon the efficiency of theoriginal refining operation, the usual range being between and The total fattyY material of the black grease, which includes both fatty acids and neutral oil, will ordinarily be approximately 92A to 93%. This also includes the unsaponiables which will range from about 2 to 6%, corn oil It is, however, frequently black grease usually containing amounts of unsaponiables in the upper portion of such range and other black greases, such as those from cottonseed oil soapstock, usually containing about 2 to 3% unsaponiables.

In present commercial practice, the black grease is employed as a source of distilled fatty acids. The black grease is usually first treated with Twitchells reagent and Water to split the contained neutral oil and liberate the combined fatty acids although in some cases the splitting is accomplished in autoclaves at elevated pressures and temperatures. The split black grease after being separated from the excess water employed in the splittingy step is then distilled at a temperature of approximately 490 F. under vacuum and withA superheated steam toarecover fatty acids. The distillation may be batch or continuous and the yield from a typical distillation may be, for example, to 85% once clistiiled fatty acids, l0 to 20% pitch and 3 to 5% loss. The once distilled fatty acids are dark in color and must be-redistilled once or more times to produce high grade fatty acids. The splitting and distilling operations are expensive and time consuming and furthermore, a substantial loss occurs due to polymerization and thermal decomposition of fatty acids at the high temperatures employed.

In accordance with the present process, the splitting operation and high temperature distillation are eliminated. The black grease is first subjected to a fractionation step involving the employment of a ivater-immiscible liquefied normally gaseous organic solvent in order to separate substantiallyV all of the gums and coloring matter from the fatty material. The fatty material separated from the impurities in this fractionation step is predominantly fatty acids and neutral oil and is a relatively light colored material. The separated fatty material is then subjected to a second fractionation step involving the employment of an aqueous solution of a. volatile water-soluble neutralizing agent for the fatty acids, such as ammonium hydroxide, or a volatile amine to neutralize the fatty acids and form water-soluble soap. This step is performed while the fattymaterial is still in solution in the liqueed waterimmiscible solvent and a. separation is easily effected between the result ing aqueous soap solution and the remaining solvent solution of neutralv oil.

The ammonia ofgthey ammonium hydroxide or the volatile amine can` be readily evaporated from the aqueous soap solution to liberate high quality fatty acids. The water in the aqueous soap solution can also be evaporated if it is desired but such water can be easily separated from the liberated fatty acids by difference in specific gravity. The ammonia or volatile amines are returned to the process for reuse.

The liquefied normally gaseous solvent can also be easily evaporated from the separated neutral oil to produce a high quality neutral oil and the solvent returned to the initial fractionation step for reuse. The liquefied solvent separated with the impurities in the initial fractionation step can also be easily evaporated therefrom and likewise returned to the initial fractionation step.

The relative yields of fatty acids and neutral oil will depend upon the relative amouts of these materials in the original black grease and in a properly conducted process the yield of both is nearly 100%. That is to say, substantially the only losses are the loss due to separation of impurities including gums and coloring matter in the initial fractionation step and this loss will usually run between 7 and 10% of the black grease. These impurities also constitute a source of valuable by-products and may be further fractionated to recover such py-products by steps forming no part of the present invention.

Although the fatty acids and neutral oil recovered from the process outlined above are both high quality products, they likewise may bc further treated to increase their purity, for example, the neutral oil is relatively high in unsaponiflables as compared to the usual crude or refined oil and may be further fractionated by a step similar to the first fractionation step of the present process to produce a portion rich in unsaponifiables and a portion low in unsaponifiables. The unsaponiflable concentrate thus obtained is a valuable source of vitamins, sterols, etc., and may be further treated to recover substantially pure materials by steps also forming no part of the present process. The fatty acids may be further purified by a fractionation step similar to the first fractionation step of the present process or by treatment with decolorizing materials. However, the fatty acids as directly produced by the two fractionation steps first described are valuable products having approximately the same value as the redistilled fatty acids produced in conventional processes of treating black grease and the neutral oil is considerably more valuable than the fatty acids. The present process is not only less expensive to carry out but also recovers fatty material in more valuable form than the conventional processes for treating black grease.

It is therefore -an object of the present invention to provide an improved process of fractionating black grease in which the fatty material is recovered in more valuable form.

Another object of the present invention is to provide a process of fractionating black grease in which large amounts of high quality neutral oil are recovered.

Another object of the invention is to provide a low cost process of treating black grease in which high grade fatty acids and high grade neutral oil are recovered and the reagents employed in the process are also recovered and reused in the. process.

A further object of the present invention is to provide an improved process of fractionating black grease in which the impurities such as gums and coloring matter are separated from 4 the fatty material in an initial step in the process and high quality fatty acids and neutral oil are recovered from subsequent steps in the process.

Other objects and advantages of the invention will appear in the following description of the invention given in conjunction with the attached drawing which is a schematic flow diagram of a process in accordance with the present invention.

Referring more particularly to the drawings, black grease may be delivered from a suitable source of supply indicated at I into a fractionating step indicated at Ii. A water---immiscible liquefied normally gaseous organic solvent may be introduced into the fractionating step from a suitable source of supply indicated at I2. The normally gaseous solvent is kept under sufficient pressure in the fractionation step II to maintain it in liquid form. The temperature of the fractionation step is maintained at a temperature above the two-phase or consolute temperature of the solvent employed and below the critical temperature of the solvent. The preferred solvent is a liquefied normally gaseous hydrocarbon such as propane and the solvent employed will be referred to as propane in the specific description of the invention. For propane the temperature maintained in the fractionation step II will range between and 105 F., the preferred range being between approximately li:J and F. The amount of propane relative to the amount of black grease will usually range from approximately 6 to approximately l5 volumes of propane per volume of black grease although larger ratios of propane to black grease may be employed.

At the temperature referred to above, the mixture of propane and black grease in the fractionation step Il separates into a lower liquid phase containing propane, gums and coloringmatter, and into an upper liquid phase containing propane, fatty acids and neutral oil. These phases may be easily separated and the propane solution of fatty acids and oil may be delivered into a second fractionation or neutralizing step I3. The lower phase .containing propane, gums and coloring matter may be delivered to an evaporation step I4 wherein the pressure is lowered to allow evaporation of propane which may be delivered in vapor form to a condensing or compression step I6 wherein the pressure on the propane is again raised to liquefy the propane after which the liquid propane is delivered back to the source of supply I2.

The preferred neutralizing agent is ammonium hydroxide and the specific process will be described with reference to this agent. An aqueous solution of ammonium hydroxide may be delivered into the neutralizing step i3 as indicated by the line I'I and admixed with the propane solution of fatty acids and cil therein, The ammonium hydroxide neutralizes the fatty acids to form ammonium soaps which dissolve in the water supplied as part of the aqueous ammonium hydroxide. The material in the neutralising step I3 separates into two liquid phases, a lower aque-- ous phase containing water and ammonium soaps of the fatty acids and an upper solvent phase which is a propane solution of neutral oil. That is to say, the ammonium hydroxide will not attack the neutral oil under the conditions maintained in the neutralizing step I3. An excess of ammonium hydroxide is ordinarily employed and an aqueous solution of ammonium soap and ammonium hydroxide may be delivered from the neutralizing step into an evaporating step I8 wherein heat or vacuum or both are applied to vaporize ammonia from the water and soap. This ammonia may be delivered to an absorber I9 wherein it is dissolved in water to provide an ammonium hydroxide solution for return to the neutralizing step I3. The ammonia is thus recycled in the system but small amounts cf ammonia will usually be lost. for example, in water discharged from the system. Make-up ammonia may be introduced into the system as indicated by the line 20.

The removal of ammonia from the materials in the evaporating step I8 leaves fatty acids and water which readily separate into two phases. The upper or fatty acid phase may be discharged from the process as light colored fatty acids, as indicated by the line 2i, and the lower or water phase may be discharged from the process as indicated by the line 22.

The upper phase from the neutralizing step I3, namely, the solution of neutral oil in liquid propane, may be delivered to subsequent steps for separation of the propane from the neutral oil. Since this solution will ordinarily contain a small amount of ammonium soaps and ammonium hydroxide solution. it is usually desirable to wash the solution prior to separating the propane from the neutral oil so that propane substantially free of ammonia may be returned to the initial fractionation step. Thus, the propane solution of neutral oil will ordinarily be delivered into a washing step 23 and admixed with water also delivered into the washing step 23 as indicated at 24. The materials in the washing step 23 readily separate into two phases, the lower phase being largely water containing a small amount of ammonium soaps and ammonium hydroxide. This lower aqueous phase, as indicated by the line 26, may be returned to the absorption step I9 to form the aqueous ammonium hydroxide which is returned to the neutralizing step I3. Any ammonium hydroxide or ammonium soaps separated from the neutral oil are thereby returned to the process and the fatty acids of said ammonium soaps are eventually recovered in the evaporation step I8.

The upper phase from the washing step 23 may be delivered into an evaporation step 21 wherein the propane is evaporated from the neutral oil and returned to the condensing step I6 as indicated by the line 28. Neutral oil may be discharged from the evaporating step as indicated by the line 29.

Each of the steps indicated in the now diagram of the drawing may be either batch or continuous. That is to say, the black grease and propane may be mixed mechanically while under pressure in a batch operation in the fractionation step II and then the mixture allowed to stand so as to settle into two phases. In a batch operation the lower phase will usually still contain a substantial amount of neutral oil and fatty acids. By adding additional propane to the separated lower layer and repeatedly fractionating this material in the manner just described, a final lower layer substantially free of neutral oil can be obtained, the various upper layers being delivered to the neutralizing step. In the neutralizing step I3, the solution of fatty acids and oil in propane may be mechanically admixed with the ammoniurn hydroxide solution and the resulting mixture allowed to stand until the two phases separate. The various washing and evaporation steps may likewise be performed as batch operations. For example. the various propane solutions of fatty acids and oil may be withdrawn from a pressure container of the initial fractionation step leaving the final propane solution of gums and coloring matter in such container after which the pressure may be reduced in the same container to evaporate the propane, leaving the gums and coloring matter which may then later be withdrawn from such container. Alternately, the solution of impurities may be first withdrawn from the container and the remaining upper layer treated with ammonium hydroxide in the container.

A continuous operation is, however, preferred. That is to say, the fractionation step II may be carried out in a suitable tower such as a packed tower in which the black grease is continuously introduced into an upper portion of the tower and liquefied propane continuously introduced into a lower portion of the tower. A propane solution of fatty acids and oil may be continuously withdrawn from the top of the tower and continuously introduced into the neutralizing step I3 which may also be carried out in a suitable tower. The aqueous solution of ammonium hydroxide may be continuously introduced into the upper portion of such tower while an aqueous solution of soap and ammonium hydroxide is continuously withdrawn from the bottom of the tower and a propane solution of neutral oil continuously withdrawn from the top of the tower. In a similar manner, continuous washing can be carried out in the washing step 23 by introducing the propane solution of neutral oil into a lower portion of the tower and wash Water into an upper portion of the tower while the used wash water is continuously withdrawn from the bottom of the tower and the washed `propane solution of neutral oil continuously withdrawn from the top of the tower. The various evaporation, absorption and condensing steps may likewise be carried out in suitable apparatus to provide continuous operation with the various materials being continuously introduced and withdrawn from such apparatus. In general, a more complete separation of impurities such as gums and coloring matter from the propane solution of fatty acids and oil can be accomplished in a continuous operation employing a fractionation tower and more complete separation can be accomplished in the neutralizing and washing steps if these steps are carried on continuously in towers.

It will be appreciated that the fractionation step I I must be operated under relatively high pressure at the temperatures mentioned above. That is to say, the pressure in the fractionation step must be suficient to maintain the propane in liquid form at the temperatures required and such pressures may range from approximately 500 to 600 pounds per square inch gauge for propane. Heating of the materials for the fractionation step Il may be either accomplished by supplying heat to the container employed for the fractionation step II or the material may be heated before being delivered into such container, for example, by indirect heat exchange in stream ow during introduction into the fractionation step II.

The other steps in the process may be carried out at substantially atmospheric temperature so that high pressures are not required to maintain the propane in liquid form. For example, the pressure may be reduced in the evaporating step I4 toatmosphericfpressnre or :helowr-.iandsthe ply `heat to the evaporation stepszIcto supply the latent heat of-thelevaporating propane.

The neutralizationl step il 3' :may lalsol :be rperformed at substantiallyuatinospherlctempera- `ture, i. e., temperatures rangingwfromilto 120 F., and the coolingof the propane. solutionoof fatty acids and oil .may-@he accomplished Aby. in-aA direct heat exchange. duringwstream idiowfabetween the fractionationstep IIfanJd the. neutralizing stepy I3. Evaporationaloffpropane due: to reduction of pressure in a batch neutralizing step I3 or'heforemtroduetionl into aicontinuous` neutralization step :maycihoweverfbe employed to reduce the I temperaturev inzthe I neutralieingystep l 3. :i Any propane thus evaporated: will, ofcourse,

I be returned tdthecondensingisten. I E. for reuse. in the. process. u

' The process illustrated specifically in the drawing is subjectttoiconsiderable variation; y.liorfexample, in a eontinuousnoperation the :washing kandr neutralizing steps maybecarried4 onlin a single tower loylntroducing the `propane' solution` ofl fatty acids .and oil 'into a lower portion of'lthe tower, introducing a concentrated ammonium `hydroxide solutionl intopan intermediate portion of the` tower and. introducingwash weten into an upper portion of the'towerr u In such an` operation, a portion of thewatcr mayalso be `evaporated in the evaporation sstep. 18 soLthataqueousammonium hydroxide is condensedin thestep I9 for return tothe neutralizing andwashingastep.. The

I fatty. acidsdelivereddrom the"evaporation,stepv I8 may be subjected;l to `furtlxer"steps for further puriflcationthereof. h That is to say, the fatty acids maybe againiadmixediwith liquefied propane and .subjected tota high :temperaturathigh pressure fractionation step similar; tothe stepi Il to remove small amounts of coloring .material not removed in Ythe fractionationfstep vI I. As an alternative.. the fatty .acids may,J be :treated with a,` deeolorizingaagent vsuohlas a bleaching adsorbent, .either while.` in` .solution in f liquefied propane or without the addition of propane thereto.V Treating of'ithe fatty, acids with fallaleaching adsorbent such asacidtreated olas',` fullers earth or activated 4chamoal,.l whi1e;in `solution in ,liquid propane is a preferred operation since rt does-not require highv .temperatures .and :thigh i pressures, any residual coloring,matter` is .effectively re moved and the Ylosses of fatty acidsfare negligible since the propane holds the fatty acids in solution and prevents theiradsorptlon by thefbleaching argent. `After 'separationofz the-propane solution of fatty acids fromrthleV solidrbleachingiagentuthe propane may be"evaporatedandreturned to the process.

In addition tothe fact that ythepresent process recovers substantially 4all ofrthe fatty acidsand neutral oil asxhigh" quality products, amaior advantage of lthe` process is. thats the `fatty acids recovered are.. substantiallyV freeV of unsaponiables. The u nsaponifialales4 are the i most: ssoluble. ofany' of the materials in the liquidpropane i and :substantially all of` vthe unsaponiablesaare present in'` the neutralnil. discharged' from the vlprooessVas indicated byutheline 29. As stated above, this neutral oil may be subjected:to a .further-r fractionation estepoessentiallyusimilar to Vthe.atractionation-step I I. `-Byinoreanslng thetemperature .so as to.approachzthecritical.:tempera- .;.ture, a.: .relatively .ismallpupperfractiomean l be i8 zesaponflables. along 4'with a lower majorx fraction `wha-'ving a: very -low rcontent of unsaponifiables :These-fractions may. beiseparated andthe fracltion rich in. unsaponiflables is a valuable source offvitaminssterols, etc.

ClottorlseedA oilblack zgrease,v which is a black wfoul-smelling material, isiperhaps the most didifucult to treati of any of the black greases. The `epi-esentiinyentionean be employedplhowever, to

10 `reeoverhigh quality. fatty Vacids andfneutral oil :from cottonseed oil blank grease. As a specific `example;ofthe presentinventiom a cottonseed oil black was admixed under pressure with 8 volumes of `liquefied propane .perrvolurne of black greasefin a pressure container.` `The materials ixrlthe container `.verethen heated to 180' F., .when a separation into adarklcolored lower layer `wand a light colored upper 'layer' occurred. IEhe upper layer wasv removed while stillheing maintained under pressure andxcooled tol05" F. A sample of this material from which the propane was Vevaporatedhad a color of 21 FAC. The i fractionation operation was repeated on the .lower Vlayer until the neutral oil and. fatty acids .were substantially. all separated therefrom and l the propane was evaporated from the final lower layer leaving a residue representing approximately 9.3 9a of the original black grease and having alcolor too darkto read.

The `several upper :layers were comhinedpcooled to 105n F. and then admired with a; concentrated ammoniumhydroxide solution (28% NH3) in exl cess. of. that required to neutralize the fatty acids. The mixing was accomplished by stirring `mechanically While themixture was maintained `under pressure sufficient. to .prevent` evaporation of propane. A White flooculent precipitate formed which settled rapidly when agitation` was discontinued to produce a lower aqueous layer in Ythe form of an aqueous solution of ammonia soap and excess znnmonium hydroxide. VThe upper layer-was alight colored solution of neutral ol in propane and was Wlthdrawnfwashed .with vwater while still under pressure and' the .15 propane then evaporated. A light colored oil was obtained, i. e., `the color was 85Y-18R Lovibond. i The yield of oil was 25% of the original black grease and this oil was of a quality'which is .sold as a premium vcrude cottonseedoil. It contained 1.5% free fatty acids and'2.5%. unsaponiilables. Ammonia was distilled from the'lower aqueous layer and the resulting fatty acid layer separated from the vvaterlayer. The fatty acidswere light in color and the yield was` 66.7%1 of `.the original black grease.

Propane isthe `preferred liquefied .normally gaseous solvent Vbecause ofits availability and cheapness and the fact that it otherwisefhas the desired characteristicsbut there arealarge number of other organic solvents `including other lsaturated and unsaturated hydrocarbons and `halogenated hydrocarbons vwhich lhave boiling points and critical temperatures inthe requisite ranges as well as rims'iscibilitywith WaterI and Einertioess 'to the materials being fractionated, and which produce two-phase systems with black grease at temperatures somewhat below their critical temperatures. Examples of ^.such other `solvents are butanepropone, ethyl chloride. methylene fluoride, 4clichlor diuor methane,.etc. l Various admixtures of saidsolvents maylikewise be employed. The .usabletemperature and pressure to produce .the desired fractionation will. of course, varydepending upon .the solvent but in aobtainedilmvlng. axhighreoncentration. orcunrfufgeneral, ithectemperaturenwilt be :.:eloseto but somewhat below the critical temperature and the pressure will be sufcient to maintain the solvent in liquid form. Also the amounts of solvent will vary with the nature of the solvent employed but will usually range between approximately 6 and 15 volumes of solvent per volume of black grease in the initial fractionation step and Will also range from approximateyl 6 to l5 volumes per volume of fatty acids and neutral oil in the neutralizing step.

Also, ammonia in the form of ammonium hydroxide is the preferred volatile neutralizing agent also because of its cheapness, availability and the excellent results obtained, but in general, the volatile water-soluble amines such as ethylamine, propylamine, butyl ami-ne. isobuytl amine. isopropyl amine and various admixtures thereof including admixtures with ammonium hydroxide may be employed. The amount of neutralizing agent employed will usually be in substantial excess of the fatty acids, for example, to 20%.

I claim:

1. The process of recovering fatty acids and neutral oil from black grease, which comprises, forming a mixture of said black grease with several times its volume of a water-immiscible liquefied normally gaseous organic solvent for said black grease at an elevated temperature above the consolute temperature of said mixture and below the critical temperature of said solvent while maintaining said mixture under sufficient pressure to retain said solvent in liquid form, whereby a lighter phase containing fatty acids and neutral oil in solution in said solvent and a heavier phase containing gums and coloring matter in solution in said solvent are produced, separating said phases from each other, admixing the separated lighter phase with an aqueous solution of a volatile water-soluble neutralizing agent reacting with said fatty acids to form water-soluble soaps while said lighter phase still contains the solvent separated therewith and is under sufiicient pressure to maintain its contained solvent in liquid form, whereby a solvent phase containing neutral oil in solution in said solvent and an aqueous phase containing said soaps and excess reagent in solution in water are produced, separating said solvent phase and aqueous phase from each other, evaporating solvent from said solvent phase to recover neutral oil and evaporating neutralizing agent from said aqueous phase to recover fatty acids.

2. The process defined in claim ll in which the amount of said solvent in said mixture of black grease and solvent is between. 6 and 15 volumes per volume of black grease.

3. The process as defined in claim 2 in which said solvent is a liquefied normally gaseous hydrocarbon.

4. The process as defined in claim 3 in which said solvent is propane.

5. The process as defined in claim 4 in which said temperature is between approximately 150 and 195 F.

6. The process as defined in claim 5 in which said temperature is between 172 and 190 F.

7. The process as defined in claim 1 in which said neutralizing agent is selected from the group consisting of ammonium hydroxide and Watersoluble volatile amines.

8. The process as defined in claim 3 in which said neutralizing agent is selected from the group consisting of ammonium hydroxide and watersoluble volatile amines.

9. The process as defined in claim 5 in which said neutralizing agent is selected from the group consisting of ammonium hydroxide and watersoluble volatile amines.

l0. The process as defined in claim 5 in which the temperature during separation of said solvent phase and said aqueous phase is between 60 and 120 F.

1l. The process as defined in claim l in which the solvent evaporated from said solvent phase is reused in the process to dissolve additional amounts of black grease and the neutralizing agent evaporated from said aqueous phase is reused in the process to treat additional amounts of said lighter phase.

l2. The process of recovering fatty acids and neutral oil from black grease, which comprises, forming a mixture of said black grease and from approximately 6 to l5 volumes of propane at a temperature between 150 and 195 F. and under sufficient pressure to maintain said propane in liquid form, whereby a lighter phase containing fatty acids and neutral oil in solution in liquid propane and a heavier phase containing gums and coloring matter in solution in liquid propane are produced, separating said phases and admixing an aqueous solution of ammonium hydroxide with said lighter phase in an amount in excess of that required to neutralize said fatty acids while said lighter phase still contains the propane separated therewith and is under suiiicient pressure to maintain its contained propane in liquid form, whereby a solvent phase containing neutral oil in solution in liquid propane and an aqueous phase containing ammonium soaps of said fatty acids in aqueous solution are produced, separating said solvent phase from said aqueous phase, evaporating propane from said solvent phase to recover neutral oil and evaporating ammonia from said aqueous phase to recover fatty acids.

13. The process as defined in claim 12 in which the temperature during separation of said solvent phase and said aqueous phase is between 60 and F.

14. The process as deiined in claim 12 in which propane is also evaporated from said heavier phase and said propane as well as the propane evaporated from said solvent phase is liquefied by pressure and mixed with additional black grease in said process and said ammonia evaporated from said aqueous phase is returned as ammonium hydroxide and admixed with additional amounts of said lighter phase in said process.

l5. The process as defined in claim 12 in which the separated solvent phase is washed with water prior to evaporation of propane therefrom.

16. The process of recovering fatty acids and neutral oil from black grease, which comprises, forming a mixture of said black grease with several times its volume of a water-immiscible liquefied normally gaseous organic solvent at an elevated temperature above the consolute temperature of said mixture and below the critical temperature of said solvent While maintaining said mixture under sufficient pressure to retain said solvent in liquid form, whereby a heavier phase containing gums and coloring matter in solution in said solvent and a lighter phase containing fatty acids and neutral oil in solution are produced, separating said phases from each other and admixing said lighter phase with an excess of neutralizing agent selected from the group consisting of an aqueous solution of ammonium hydroxide and aqueous solutions of water-soluble volatile amines while said lighter phase still contains the solvent separated therewith and is under suiiieient pressure to maintain its contained solvent in liquid form, whereby a solvent phase containing neutral oil in solution in said solvent and an aqueous phase containing soaps of fatty acids and said agent and excess agent, in aqueous solution are produced, separating said solvent phase and said aqueous phase from each other, vaporizing said agent from said aqueous phase to recover fatty acids therefrom and reusing said agent for neutralizing additional amounts of said solvent phase, and vaporizing said solvent from the separated solvent phase to recover neutral oil and from said heavier phase to recover said iml2 puritiesiand` reusingfsaddsolvent in said process for admixture `with additional amounts of black grease.

' MORRIS MATTIKOW.

References tilted. in the file of this patent 'UNITED BTAIES PATENTS Number Name Date 10 2,007,166 Hund et al. July 9, 1935 2,219,652 Hixson et al. Oct. 29, 1940 2,480,564 Forney Aug. 30, 1949 

1. THE PROCESS OF RECOVERING FATTY ACIDS AND NEUTRAL OIL FROM BLACK GREASE, WHICH COMPRISES, FORMING A MIXTURE OF SAID BLACK GREASE WITH SEVERAL TIMES ITS VOLUME OF A WATER-IMMISCIBLE LIQUEFIED NORMALLY GASEOUS ORGANIC SOLVENT FOR SAID BLACK GREASE AT AN ELEVATED TEMPERATURE ABOVE THE CONSOLUTE TEMPERATURE OF SAID MIXTURE AND BELOW THE CRITICAL TEMPERATURE OF SAID SOLVENT WHILE MAINTAINING SAID MIXTURE UNDER SUFFICIENT PRESSURE TO RETAIN SAID SOLVENT IN LIQUID FORM, WHEREBY A LIGHTER PHASE CONTAINING FATTY ACIDS AND NEUTRAL OIL IN SOLUTION IN SAID SOLVENT AND A HEAVIER PHASE CONTAINING GUMS AND COLORING MATTER IN SOLUTION IN SAID SOLVENT ARE PRODUCED. SEPARATING SAID PHASES FROM EACH OTHER, ADMIXING THE SEPARATED LIGHTER PHASE WITH AN AQUEOUS SOLUTION OF A VOLATILE WATER-SOLUBLE NEUTRALIZING AGENT REACTING WITH SAID FATTY ACIDS TO FORM WATER-SOLUBLE SOAPS WHILE SAID LIGHTER PHASE STILL CONTAINS THE SOLVENT SEPARATED THEREWITH AND IS UNDER SUFFICIENT PRESSURE TO MAINTAIN ITS CONTAINED SOLVENT IN LIQUID FORM, WHEREBY A SOLVENT PHASE CONTAINING NEUTRAL OIL IN SOLUTION IN SAID SOLVENT AND AN AQUEOUS PHASE CONTAINING SAID SOAPS AND EXCESS REAGENT IN SOLUTION IN WATER ARE PRODUCED, SEPARATING SAID SOLVENT PHASE AND AQUEOUS PHASE FROM EACH OTHER EVAPORATING SOLVENT FROM SAID SOLVENT PHASE TO RECOVER NEUTRAL OIL AND EVAPORATING NEUTRALIZING AGENT FROM SAID AQUEOUS PHASE TO RECOVER FATTY ACIDS. 